error: this call to `hash` on the unit type will do nothing
  --> $DIR/unit_hash.rs:19:23
   |
LL |         Foo::Empty => ().hash(&mut state),
   |                       ^^^^^^^^^^^^^^^^^^^ help: remove the call to `hash` or consider using: `0_u8.hash(&mut state)`
   |
   = note: the implementation of `Hash` for `()` is a no-op
   = note: `-D clippy::unit-hash` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::unit_hash)]`

error: this call to `hash` on the unit type will do nothing
  --> $DIR/unit_hash.rs:26:5
   |
LL |     res.hash(&mut state);
   |     ^^^^^^^^^^^^^^^^^^^^ help: remove the call to `hash` or consider using: `0_u8.hash(&mut state)`
   |
   = note: the implementation of `Hash` for `()` is a no-op

error: this call to `hash` on the unit type will do nothing
  --> $DIR/unit_hash.rs:31:5
   |
LL |     do_nothing().hash(&mut state);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `hash` or consider using: `0_u8.hash(&mut state)`
   |
   = note: the implementation of `Hash` for `()` is a no-op

error: aborting due to 3 previous errors